U.S. patent application number 10/228487 was filed with the patent office on 2004-03-04 for resin compositions for producing biaxially oriented polypropylene films.
Invention is credited to Kim, Sehyun, Stephans, Michael Robert.
Application Number | 20040041299 10/228487 |
Document ID | / |
Family ID | 31976039 |
Filed Date | 2004-03-04 |
United States Patent
Application |
20040041299 |
Kind Code |
A1 |
Kim, Sehyun ; et
al. |
March 4, 2004 |
Resin compositions for producing biaxially oriented polypropylene
films
Abstract
Polypropylene resin compositions are provided that are useful in
the production of biaxially oriented polypropylene films (BOPPs).
The resins of the present invention are blends of high crystalline
(low solubles) polypropylene homopolymer and an ethylene/propylene
random copolymer (RCP). These blends can be used to replace
standard high solubles BOPP grade polypropylene homopolymers. In
addition, the use of high crystalline polypropylene homopolymers in
the blends imparts improved stiffness to the finished films while
maintaining good processability of the blends.
Inventors: |
Kim, Sehyun; (Murrysville,
PA) ; Stephans, Michael Robert; (Pittsburgh,
PA) |
Correspondence
Address: |
Robert A. Koons, Jr.
BUCHANAN INGERSOLL P.C.
Eleven Penn Center, 14th Floor
Nineteenth and Market Streets
Philadelphia
PA
19103-2985
US
|
Family ID: |
31976039 |
Appl. No.: |
10/228487 |
Filed: |
August 27, 2002 |
Current U.S.
Class: |
264/176.1 ;
525/240 |
Current CPC
Class: |
C08L 23/10 20130101;
C08L 23/12 20130101; Y10S 264/90 20130101; C08L 23/14 20130101;
Y10S 264/901 20130101; C08L 23/10 20130101; C08J 2323/10 20130101;
Y10T 428/31855 20150401; Y10T 428/31909 20150401; C08J 5/18
20130101; Y10S 264/902 20130101; C08L 2666/06 20130101; C08L
2666/06 20130101; C08L 23/12 20130101 |
Class at
Publication: |
264/176.1 ;
525/240 |
International
Class: |
C08L 023/00; C08L
023/04 |
Claims
What is claimed is:
1. A resin composition suitable for processing into a biaxially
oriented polypropylene film, the composition comprising: about 70%
to about 95% by weight of a polypropylene homopolymer, said
polypropylene homopolymer having less than 3% by weight xylene
solubles; and about 5% to about 30% by weight of an
ethylene/propylene copolymer, said ethylene/propylene copolymer
containing from about 0.5% to about 7.0% ethylene by weight.
2. The resin composition according to claim 1, wherein said
polypropylene homopolymer has a crystallinity of at least 55%.
3. The resin according to claim 1, wherein said resin is produced
by in reactor blending.
4. The resin composition according to claim 1, further comprising
at least one additive selected from the group consisting of:
nucleators, anti-oxidants, acid neutralizers, slip agents,
antiblock, antifogging agents and pigments.
5. The resin composition according to claim 1, wherein said
composition comprises about 70% to about 85% of a polypropylene
homopolymer having less than 3% by weight xylene solubles, and
about 15% to about 30% by weight of an ethylene/propylene
copolymer, said ethylene/propylene copolymer containing from about
0.5% to about 7.0% ethylene by weight.
6. A biaxially oriented polypropylene film comprising: about 70% to
about 95% by weight of a polypropylene homopolymer, said
polypropylene homopolymer having less than 3% by weight xylene
solubles; and about 5% to about 30% by weight of an
ethylene/propylene copolymer, said ethylene/propylene copolymer
containing from about 0.5% to about 7% ethylene by weight.
7. The biaxially oriented polypropylene film according to claim 6,
wherein said polypropylene homopolymer has a crystallinity of at
least 55%.
8. The biaxially oriented polypropylene film according to claim 6,
further comprising at least one additive selected from the group
consisting of: nucleators, anti-oxidants, acid neutralizers, slip
agents, antiblock, antifogging agents and pigments.
9. The biaxially oriented polypropylene film according to claim 6,
wherein said composition comprises about 70% to about 85% of a
polypropylene homopolymer having less than 3% by weight xylene
solubles, and about 15% to about 30% by weight of an
ethylene/propylene copolymer, said ethylene/propylene copolymer
containing from about 0.5% to about 7.0% ethylene by weight.
10. A method of producing a biaxially oriented polypropylene film,
the method comprising: providing a resin composition comprising:
about 70% to about 95% by weight of a polypropylene homopolymer,
said polypropylene homopolymer having less than about 3% by weight
xylene solubles, and about 5% to about 30% by weight of an
ethylene/propylene copolymer, said ethylene/propylene copolymer
containing from about 0.5% to about 7% ethylene by weight;
extruding said resin composition into a cast sheet; and stretching
said cast sheet in a first machine direction, and stretching said
cast sheet in a second transverse direction, to produce a biaxially
oriented film.
11. The method according to claim 10, wherein said stretching in a
first machine direction and said stretching in a second transverse
direction are performed simultaneously.
12. The method according to claim 10, wherein said stretching in a
first machine direction and said stretching in a second transverse
direction are performed consecutively.
13. The method according to claim 12, wherein said stretching is
performed on a tenter frame apparatus.
14. The method according to claim 13, wherein said stretching in
said first machine direction is performed at a temperature of from
about 60.degree. C. to about 140.degree. C. and said stretching in
said second transverse direction is performed at a temperature from
about 130.degree. C. to about 170.degree. C.
15. The method according to claim 10, wherein said resin
composition further comprises at least one additive selected from
the group consisting of: nucleators, anti-oxidants, acid
neutralizers, slip agents, antiblock, antifogging agents and
pigments.
16. The method according to claim 10, wherein said resin
composition comprises about 70% to about 85% of a polypropylene
homopolymer having less than 3% by weight xylene solubles, and
about 15% to about 30% by weight of an ethylene/propylene
copolymer, said ethylene/propylene copolymer containing from about
0.5% to about 7.0% ethylene by weight.
17. A method of producing a biaxially oriented polypropylene film,
the method comprising: providing a resin composition comprising:
about 70% to about 95% by weight of a polypropylene homopolymer,
said polypropylene homopolymer having less than about 3% by weight
xylene solubles, and about 5% to about 30% by weight of an
ethylene/propylene copolymer, said ethylene/propylene copolymer
containing from about 0.5% to about 7% ethylene by weight;
extruding said resin composition into a tube; and stretching said
tube in a first machine direction, and inflating said tube with a
gas to stretch said tube in a second transverse direction, to
produce a biaxially oriented film.
Description
FIELD OF THE INVENTION
[0001] The present invention is drawn generally to the field of
polypropylene resins. More specifically, the present invention is
drawn to the field of polypropylene resins for the manufacture of
biaxially oriented polypropylene films.
BACKGROUND OF THE INVENTION
[0002] BOPP (biaxially oriented polypropylene) film is produced by
drawing a cast sheet of polypropylene in two directions at a
temperature below the melting temperature of the resin. Specific
characteristics are required for the standard polypropylenes used
to produce BOPP materials, such as relatively larger amounts of
xylene solubles, and relatively low isotacticity. It is known that
for a given PP, the lower the isotacticity, the lower the melting
temperature of the PP and the better its processability to BOPP
film. However, these same properties in the PP result in poorer
properties of the resulting film. Therefore, there exists a
processability-property trade-off in BOPP materials. In addition,
production of high solubles materials generally used for BOPP films
is not easy because it requires a specific catalyst system and
careful handling of powder. It is known that it is difficult to
produce a homopolymer containing xylene solubles fractions higher
than 6% because a specific catalyst system as well as careful
handling of polymer powder in the reactor are required. In general,
the large amounts of xylene solubles in the polypropylene become
sticky and often cause agglomeration of polymer powder in the
reactor, disrupting continuous production at the plant.
[0003] To avoid the problems of producing high solubles material,
blends that improve the processability of low solubles material
have been investigated. It is well known that isotactic PP (iPP)
produced by a Ziegler-Natta (ZN) catalyst has a broad isotacticity
and molecular weight distribution, thus exhibiting a broad melting
temperature range. Conversely, PP produced by a metallocene
catalyst exhibits narrow isotacticity and molecular weight
distribution and thus, the melting temperature range is relatively
narrow. Unlike PP produced by ZN catalyst, some degree of
regio-mis-insertion, i.e., "head-to-head" or "tail-to-tail"
insertions, of monomer exists in the metallocene isotactic PP
(m-iPP). The melting temperature of m-iPP is also affected by the
degree of regio-mis-insertion in addition to isotacticity. Thus, an
iPP of much lower melting temperature than conventional ZN-iPP can
be produced with a metallocene catalyst. When employed in BOPP
film, however, a much narrower temperature window for drawing is
available due to the narrow tacticity and molecular weight
distribution.
[0004] The effect of the addition of m-iPP to ZN-iPP on BOPP film
was explored by Phillips et al, J. of Applied Polymer Science, 80,
2400 (2001). It was found that the addition of m-iPP to ZN-iPP
provides a balance of elevated temperature draw performance and
room temperature film properties relative to the ZN-iPP materials.
Improved processability of the BOPP film including fewer webs
breaks and drawability at higher line speeds have been claimed by
the addition of some amounts of metallocene syndiotactic PP to
ZN-iPP in U.S. Pat. No. 6,207,093 to Hanyu, Mar.27, 2001, Fina
Technology. The addition of some amounts of modifier tends to
improve processability of iPP and/or properties of the resulting
film. The selection of the modifier depends on the desired film
properties and availability of modifier.
[0005] In U.S. Pat. No. 5,691,043, to Keller et al addition of
various atactic and syndiotactic polypropylenes, as well as various
propylene copolymers to a standard BOPP grade isotactic
polypropylene homopolymer to produce a core layer for multi-layer a
uni-axially shrinkable film is discussed. However, Keller does not
discuss the possibility of replacing standard BOPP grade
polypropylene homopolymers with low soluble content material.
[0006] In addition to seeking replacements for high solubles
polypropylenes, BOPP film manufacturers have long sought a material
that provides a stiffer oriented film while maintaining acceptable
stretchability. High crystalline PP materials impart the desired
stiffness to the finished articles, however, these materials are
generally not suitable for processing into BOPP films. This poor
operability of high crystalline materials is reported in U.S. Pat.
No. 5,691,043.
[0007] It would be desirable to provide a resin composition
suitable for producing BOPP films that has both good processability
and imparts the desired characteristics to the finished film. It
would further be desirable to provide a resin for producing BOPP
films that avoids the problems associated with producing high
soluble content PP homopolymers. Such compositions could also
comprise a high content of high crystalline polypropylene
homopolymer to impart greater stiffness to the material.
SUMMARY OF THE INVENTION
[0008] The present invention provides blends of non-BOPP grade
polypropylene homopolymers with ethylene/propylene random
copolymers. The compositions comprise from about 70% to about 95%
of a non-BOPP grade polypropylene homopolymer and from about 5% to
about 30% of an ethylene/propylene random copolymer. The blends
allow the use of polypropylene homopolymers having a higher
crystallinity (lower solubles content) than would otherwise be
necessary for processing into BOPP films.
[0009] The compositions according to the current invention can be
produced either by melt blending of separate resin powders or by an
in-situ in reactor blending process during production of the
polymers.
BRIEF DESCRIPTION OF THE FIGURES
[0010] FIG. 1 shows the T.M. Long Yield Stress of various compounds
as a function of temperature.
[0011] FIG. 2 shows the T.M. Long yield stress stretched at 280 and
290.degree. F. as a function of cast sheet density.
[0012] FIG. 3 shows the thermal fractionation endotherms of HCPP
(FF050HC) and its blend with 30% RCP in comparison to FF029A
(31J026).
[0013] FIG. 4 shows the T.M. Long Yield Stress of various compounds
as a function of temperature.
[0014] FIG. 5 shows the T.M. Long yield stress stretched at 280 and
290.degree. F. as a function of cast sheet density.
[0015] FIG. 6 shows the Tensile Stress of films made from various
resins.
[0016] FIG. 7 shows the Tensile Modulus of films made from various
resins.
[0017] FIG. 8 shows the Haze of films made from various resins.
[0018] FIG. 9 shows the % Transmittance of films made from various
resins.
[0019] FIG. 10 shows the 45 degree gloss of films made from various
resins.
[0020] FIG. 11 shows the Shrinkage of films made from various
resins.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The resin compositions according to the current invention
are blends of non-BOPP grade polypropylene homopolymers and
ethylene/propylene random copolymers. The blends according to the
current invention may be produced either by melt blending separate
powders or by producing the blend in-situ in an in reactor process.
In either case, the blends according to the current invention
display processing characteristics that are comparable to or better
than standard BOPP grade polypropylene homopolymers. Additionally,
films made with resins according to the current invention display
improved qualities in terms of haze, gloss and stiffness over films
produced using standard BOPP grade polypropylene homopolymers.
[0022] Films comprising the resins according to the current
invention can be made by any commercial process for producing films
comprising standard BOPP grade homopolymers. For example, two
prevalent commercial processes for producing oriented films are the
tenter frame process and the "bubble" or blown film process.
[0023] In a typical tenter frame process, molten polymer is
supplied to a flat slot die, from which a cast sheet or film is
extruded. This cast sheet or film is then conveyed to a chill
roller where it is cooled to a suitable temperature. The cast sheet
or film is then conveyed to a pre-heat roller where it is heated to
an appropriate stretching temperature. Stretching in the machine
direction is accomplished by means of a pair of sequential rollers.
The first, slow roller is followed by a second fast roller that
rotates at a speed sufficient to generate a surface speed that is
typically 4-7 times faster than the slow roller. The speed
differential between the fast and slow rollers causes a 4-7 fold
stretching of the cast sheet or film in the machine direction.
After stretching in the machine direction, the film is then cooled
again by additional chill roller(s) before being conveyed to a
second pre-heat roller where it is heated to an appropriate
temperature for stretching in the transverse direction. The
transverse stretching section of the tenter frame then stretches
the film by means of a plurality of tenter clips, which grasp the
opposite sides of the film and stretch it in a lateral direction.
The concluding portion of the stretching process may include an
annealing section. After chilling to an appropriate temperature",
the film is then trimmed of waste and then applied to take up
spools.
[0024] The typical steps involved in the bubble or blown film
process include extruding the molten polymer is through an annular
die and quenching in water to form a calibrated tube. The tube is
then conveyed to the orientation tower where it is reheated to the
optimum temperature for orientation. At the top of the tower, the
tube is squeezed airtight by the first stretching nip. The tube is
then heated and inflated with high-pressure air to form a large
diameter bubble. The bubble orients the film in the transverse
direction while simultaneously, the bubble is stretched in the
machine direction by the speed differential between the first and
second stretching nips. The oriented bubble is then collapsed by
converging rolls and then annealed. After annealing, the film is
slit into two webs. Each web is corona treated or flame treated and
then wound.
[0025] Those skilled in the art will recognize that these examples
of a tenter frame and bubble process are for illustrative purposes
only. Variations on either process are within the knowledge of one
skilled in the art and are considered to be within the scope of the
present invention. Further, films produced using the resin
compositions according to the current invention are not limited to
those produced by either the tenter frame or bubble process. The
resin compositions according to the current invention are useful in
the production of BOPP films generally and are not limited to the
specific methodology disclosed herein.
[0026] The resin compositions according to the current invention
comprise from about 70% to about 95% of a low solubles
polypropylene homopolymer and from about 5% to about 30% of an
ethylene/propylene random copolymer. Preferably, the resin
compositions according to the current invention comprise from about
70% to about 85% of a low solubles polypropylene homopolymer and
from about 15% to about 30% of an ethylene/propylene random
copolymer (RCP).
[0027] Polypropylene homopolymers that are suitable to be used in
the compositions according to the current invention have a
crystalline content of at least 55%, and a solubles content less
than about 3%, preferably less than about 2%. Examples include, but
are not limited to: F020HC, F050HC from Sunoco, 3576X from AtoFina,
9433x from BPAmoco and Novolen 1040NX from Targor. The
ethylene/propylene RCPs that are suitable for use in the resin
compositions according to the current invention contain from about
0.5% to about 7% of ethylene, preferably about 2.5% ethylene.
Examples of ethylene/propylene copolymers include, but are not
limited to: TR3020F, TR3005, TR3020SF from Sunoco, 8573 from
AtoFina, 8249 from BPAmoco and 256M from Basell.
[0028] The resin compositions according to the current invention
can be produced by melt blending a low solubles polypropylene
homopolymer with an ethylene/propylene copolymer by compounding in
a known way. Preferably, the resin compositions according to the
current invention are produced in-situ in a multi reactor process.
For example, in a four reactor process, the polypropylene
homopolymer may be produced in the first two reactors. The
ethylene/propylene RCP may then be produced in the third and fourth
reactors as the homopolymer continues to polymerize. Alternatively,
in a two reactor process, the polypropylene homopolymer is made in
the first reactor and the ethylene/propylene RCP may be made in the
second reactor as the homopolymer continues to polymerize. In this
way, the ethylene/propylene RCP may be distributed more uniformly
in the blend. Although production of the blends by an in reactor
process is preferred, blends made by either method are suitable for
producing BOPP films according to the current invention.
[0029] The resin compositions and BOPP films according to the
current invention may also include a number of additives, including
but not limited to: nucleators, anti-oxidants, acid neutralizers,
slip agents, antiblock, antifogging agents and pigments.
EXAMPLE 1
[0030] Conventional Polypropylene
[0031] Several samples of a resin blend according to the current
invention were prepared using a conventional non-BOPP grade
polypropylene homopolymer having low solubles. Polypropylene
homopolymer, D022D, available from Sunoco, was melt blended with
various amounts of a random copolymer resin having 2.5% ethylene,
TR3020F, available from Sunoco. A commercial BOPP grade
polypropylene, FF020D, available from Sunoco, containing relatively
large amounts of xylene solubles, e.g., 4.9%, was included for
comparison. The various blends prepared are shown in Table 1.
1TABLE 1 Compositions Prepared Resin A B C D E F D022 100 95 90 80
TR3020 5 10 20 100 FF020D 100
[0032] The characteristics of compounds containing random copolymer
along with homopolymers and random copolymer are given in Table
2.
2TABLE 2 Characteristics of compounds containing RCP in comparison
to FF020D Property A B C D E F D022 100 95 90 80 TR3020 5 10 20 100
FF020D 100 (30H036) MFR 2.0 1.8 1.8 1.8 2.4 2.0 % XS 2.9 2.9 3.1
3.3 5.2 4.9 Mn/1000 64 64.9 65.0 65.7 65.9 66.0 Mw/1000 333 330 328
322 296 349 Mz/1000 930 912 917 874 751 1045 D 5.22 5.08 5.05 4.91
4.49 5.29 D' 2.79 2.76 2.80 2.71 2.54 -- T.sub.m (.degree. C.)
164.8 164.8 163.1 162.9 149.2 -- T.sub.c (.degree. C.) 115.0 112.5
112.1 112.0 103.4 -- % X.sub.c 58.7 57.3 57.5 56.3 45.6 53.9
Samples contain 0.15% Irgafos 168, 0.1% Irganox 1076, 0.1% Irganox
1010 and 0.025% DH0T
[0033] It is known that the isotacticity of the insoluble fraction
of polypropylene and the amounts of solubles are inversely related
and determine the crystallinity of the polymer. Thus, a random
copolymer (RCP) that has relatively lower crystallinity with larger
amounts of xylene solubles than a homopolymer could modify (or
decrease) the overall crystallinity when added to homopolymer.
Table 2 indicates that the addition of RCP slightly increases the
amounts of xylene solubles, decreases the overall crystallinity and
the recrystallization temperature. Addition of 20% RCP was not,
however, enough to decrease the overall crystallinity of the
compound to the same level as that of the standard BOPP grade
polypropylene. Based on the additive rule, it appears that about
40% RCP is required to have a comparable overall crystallinity to
FF020D.
[0034] Cast Sheet and T.M. Long Films
[0035] Cast sheets 22-23 mil thick were prepared from these
materials in Table 2 using HPM sheet line (L/D=30) under the
conditions shown in Table 3. The extruder was equipped with a flat
die for vertical extrusion. The polymer melt extruded through the
die was quenched on to a chill roll into the sheet. The temperature
of the chill roll was kept at 110.degree. F. (43.3.degree. C.).
3TABLE 3 Zone 1 2 3 4 Die 1 Die 2 Melt Temp. Temp. (.degree. C.)
204 246 260 260 260 260 263
[0036] The density of the extruded sheets was measured in a Techne
Density column containing 558 ml H.sub.2O and 322 ml isopropanol
mixture in the heavy flask and 327 ml H.sub.2O an 553 ml
isopropanol in the light flask.
[0037] For film preparation, polypropylene was extruded onto a cast
roll to produce either 0.254 or 0.508 mm thick sheet. Samples (5.08
cm.times.5.08 cm) were cut out of the sheet stock and stretched
with a T. M. Long stretcher (T. M. Long Corporation, Somerville,
N.J.). This equipment allows simultaneous and/or consecutive
biaxial orientation at an elevated temperature. Samples were
stretched with the T.M. Long at a given stretching temperature and
a fixed strain rate of 50.8 mm/sec after 25 sec. pre-heating. The
tensile biaxial stress-strain curve is simultaneously generated
during orientation. The sheets were stretched to 0.6-0.7 mil film
by simultaneous stretching at 6.2.times.6.2 draw ratio. The film
properties were determined by the method prescribed in ASTM 882.
Table 4 gives the density of the cast sheet, T.M. Long yield stress
and film properties while FIGS. 1 and 2 show the dependence of T.M.
Long yield stress on the stretching temperature and the cast sheet
density, respectively. In accordance with the overall crystallinity
of the compound, the density of the cast sheet also decreases with
increasing amounts of RCP. The T.M. Long yield stress decreases
with increasing stretching temperature and/or with decreasing the
density of the cast sheet as shown in FIGS. 1 and 2.
4TABLE 4 Density of sheet stock and T.M. Long yield stress 667A
667B 667C 667D 667E 884A Resin Composition D022 5% RCP 10% 20%
TR3020 FF020D RCP RCP (30H036) Density (cast sheet) 0.9028 0.9025
0.9017 0.9017 0.8957 0.8988 TML yield stress (psi) @ 138.degree. C.
505 494 486 458 125 404 @ 143.degree. C. 377 390 378 319 38 294 @
149.degree. C. 258 251 234 199 -- 174
[0038] It is noted that FF020D that has 4.9% xylene solubles
exhibits about 100 psi lower T.M. Long yield stress than D022 that
has 2.9% xylene solubles irrespective of the stretching
temperature. TR3020 that has 2.5% ethylene and 5.5% xylene solubles
has significantly lower T.M. Long yield stress than FF020D. It can
be attributed to the lower melting temperature and overall
crystallinity of the random copolymer along with larger amounts of
xylene solubles than the homopolymer. These results indicate that
the crystalline state at the stretching temperature dictates the
T.M. Long yield stress. It should be noted that the crystalline
state of a polypropylene at a stretching temperature predominantly
affects the viscosity of the "pseudo-melt" (because the polymer is
partially melted) along with molecular weight. Table 5 gives the
properties of film produced with T.M. Long stretcher. These results
indicate that the tensile properties and haze of the compounds are
comparable to those of homopolymer, i.e., FF020D, even at 20%
addition of random copolymer. These results indicate that the
homo-random polypropylene can be employed as an alternative BOPP
material replacing high solubles homopolymer.
5TABLE 5 Properties of film produced at 138.degree. C. by
stretching at 6.2 .times. 6.2 ratio 667A 667B 667C 667D 667E 884A
Resin Composition D022 5% RCP 10% 20% TR3020 FF020D RCP RCP
(30H036) Tensile Stress (kpsi) 27.1 31.4 31.1 30.3 21.9 27.1
Tensile Strain (%) 63.2 70.2 72.4 74 59.9 69 Modulus (kpsi) 367 370
370 254? 363 332 Haze 0.63 0.63 0.68 0.63 0.67 0.65
EXAMPLE 2
[0039] High Crystalline Polypropylene
[0040] A second set of compositions was prepared using a high
crystallinity polypropylene homopolymer, F050HC, available from
Sunoco. The random copolymer, TR3005, available from Sunoco, having
2.5% ethylene, was melt blended with the HC homopolymer via
compounding as given in Table 6. A conventional BOPP material,
FF029A, available from Sunoco, designed for the core material of
clear film, was used as a control.
6TABLE 6 Compounds prepared in this study 2100944 A B C D F050HC %
100 85 70 TR3005 % 15 30 FF029A (31J026) 100
[0041] The melting temperature and recrystallization temperature
for each composition was determined using annealed differential
scanning calorimetry (ADSC). The polymers were melted at
230.degree. C. for 5 minutes and cooled to 0C at a rate of
10.degree. C./min while recording recrystallization exotherm. Then,
the sample was heated to 190.degree. C. at a rate of 10.degree.
C./min to record the melting endotherms.
[0042] The materials were also evaluated by thermal fractionation.
The polymer melt was cooled to 170.degree. C. at a rate of
20.degree. C./min, followed by isothermal crystallization process
during which the sample was held for 4 hrs. The isothermal
crystallization process continued to decrease to 130.degree. C. at
10.degree. C. decrement. The temperature of the sample was then
decreased to 0.degree. C., and the sample was analyzed as it was
heated to 200.degree. C. at a rate of 10.degree. C./min. to record
the melting endotherm. It has been discovered that how well a
material stretches on a tenter frame depends on the shape of
endotherm recorded from the thermal fractionation. Thus, the
thermal behavior of the compositions produced were evaluated via
the thermal fractionation method as shown in FIG. 3. As can be
seen, the blend with 30% of RCP has a trace similar to that of the
standard BOPP grade material.
[0043] The characteristics of materials produced are given in Table
7. The commercial BOPP grade, FF029A that contains relatively large
amounts of xylene solubles, e.g., 5.8%, was included for
comparison. As noted in the previous Example (1), a RCP that has
2.5% ethylene has relatively lower crystallinity and larger amounts
of xylene solubles than a homopolymer. Therefore, when added to
homopolymer, a RCP should modify, i.e., decrease, the overall
crystallinity. Table 7 confirms that the addition of RCP to a
homopolymer slightly increases the amounts of xylene solubles,
decreases the overall crystallinity and the recrystallization
temperature. It is noted that the blend of F050HC with 30% TR3005
has a slightly higher crystallinity than FF029A. The molecular
weight and distributions of all the polymers are comparable within
the limit of experimental error.
7TABLE 7 Characteristics of compounds containing RCP in comparison
to FF029A A B C D 2100944 F050HC 15% TR3005 30% TR3005 FF029A
(31J026) MFR 6.2 4.6 3.7 3.0 % XS 1.73 2.28 3.12 5.82
T.sub.m(.degree. C.) 163.7 162.2 159.3 159.1 T.sub.c(.degree. C.)
118.1 115.1 112.9 112.6 % X.sub.c 61.9 58.6 55.2 53.3 Mn/1000 53.5
63.2 65.8 50.4 Mw/1000 252 278 283 257 Mz/1000 779 819 838 988 D
4.7 4.4 4.3 5.1 D' 3.1 2.9 3.0 3.8 Samples contain 0.15% Irgafos
168, 0.1% Irganox 1076, 0.1% Irganox 1010 and 0.025%
[0044] DHOT
[0045] Cast Sheets and T.M. Long Films
[0046] As in Example 1, cast sheets 22-23 mil thick sheet were
produced using HPM sheet line (L/D=30) under the conditions in
Table 8.
8TABLE 8 Zone 1 2 3 4 Die 1 Die 2 Melt Temp. Temp. (.degree. C.)
204 246 260 260 260 260 263
[0047] The temperature of the chill roll was kept at 110.degree. F.
(43.3.degree. C.). The density of the extruded sheets was measured
in a Techne Density column containing 558 ml H.sub.2O and 322 ml
isopropanol mixture in a heavy flask and 327 ml H.sub.2Oan 553 ml
isopropanol in a light flask.
[0048] The 22-23 mil sheets were stretched to 0.6-0.7 mil film by
simultaneous stretching at 6.2.times.6.2 draw ratio with T.M. Long
after 25 sec. pre-heating at a given stretching temperature. The
yield stress was measured while stretching the cast sheet.
[0049] The film tensile properties were determined by the method
prescribed in ASTM 882.
[0050] Strips (1".times.8") from T.M. Long film were used to
determine the tensile properties. Although ASTM recommends 10" grip
separation and 1 in/min crosshead speed for the measurement of
tensile modulus, 4" grip separation was employed due to the size of
the T.M. Long film. Accordingly, the crosshead speed was adjusted
to 0.4 in/min. For all other tensile properties, the crosshead
speed was 2 in/min. At least 5 specimens were tested.
[0051] Optical properties such as transparency, haze and clarity of
the film were evaluated by the method prescribed in ASTM 1003 (Haze
and % transmittance) and ASTM 1746 (clarity).
[0052] Gloss was measured at the 3 different angles, 20, 45 and 60
degree by using the method described in ASTM 2457, where 60-deg. is
recommended for intermediate gloss films, 20-deg. for high gloss
films and 45-deg. for intermediate and low gloss films.
[0053] Shrinkage was measured using ASTM D2732. A rectangular
cutout (3.9".times.3.9") from the T.M. Long film was placed in a
"Free Shrink" holder such that the cutout is free from contact with
the edge of the holder. Then, the holder was immersed in an oil
bath for at least 10 seconds at a given temperature in order for
the material to come to thermal equilibrium and undergo maximum
shrinkage. The holder was removed from the oil bath and quickly
immersed in oil at room temperature. After at least 5 seconds, the
sample was removed from the oil. After removing the remaining oil
from the specimen, the dimension of the specimen was measured and
the shrinkage was calculated using the equation:
% shrinkage=(L.sub.o-L.sub.f)/L.sub.o.times.100
[0054] where L.sub.o is the initial length and L.sub.f length after
shrinking.
[0055] Table 9 gives the density of the cast sheet, the T.M. Long
yield stress and film properties while FIGS. 4 and 5 show the
dependence of the T.M. Long yield stress on the stretching
temperature and the cast sheet density, respectively.
9TABLE 9 Density of sheet stock and T.M. Long yield stress A B C D
Resin F050HC 15% TR3005 30% TR3005 FF029A Composition Density
0.9043 0.9034 0.9026 0.9029 (Cast Sheet) T.M. Long yield stress @
138.degree. C. .sup. 779.sup.a 644 549 519 @ 143.degree. C. 594 496
418 390 @ 149.degree. C. 445 365 281 253 .sup.athe film tore during
stretching after yield.
[0056] In accordance with the overall crystallinity of the
materials, the density of the cast sheet decreases with increasing
amounts of RCP as does the T.M. Long yield stress as shown in FIGS.
4 and 5. While the T.M. Long film of FF050HC tore after yielding
when stretched at 138.degree. C., the blend containing 15% random
copolymer did not tear when stretched. It is noted that although
the blend that contains 30% random copolymer has a slightly lower
density than FF029A, its T.M. Long yield stress is higher as shown
in FIG. 5. Since the T.M. Long yield stress depends on the density,
i.e., crystallinity, of the cast sheet at the stretching
temperature, it appears that the blend containing 30% random
copolymer should have a higher density at the stretching
temperature than FF029A does.
[0057] The properties of film produced at 3 different temperatures
with a T.M. Long stretcher are given in Table 10 and depicted in
FIGS. 6-11. The results in Table 10 may be summarized as follows.
The T.M. Long films produced from the blends exhibit higher tensile
properties than those produced from FF029A. Haze and %
transmittance of the film produced from the blends at 138.degree.
C. and/or 143.degree. C. are comparable to those produced from
FF029A. However, when stretched at 149.degree. C., the film
produced from FF029A is much hazier than those from the blends. The
45-degree gloss varies depending upon the stretching temperature.
The shrinkage of the film from the blends is slightly lesser than
that from FF029A.
10TABLE 10 Properties of T.M. Long film produced at various
temperatures A B C D 2100944 F050HC.sup.a 15% TR3005 30% TR3005
FF029A 138.degree. C. Haze -- 0.90 0.58 0.63 Transmittance (%) 94.5
94.4 94.5 Clarity -- 97.4 98.1 98.0 Gloss 20 -- 36.1 27.2 41.0 45
-- 93.1 90.3 93.7 60 -- 129.7 114.2 114.2 Tensile stress (kpsi) --
31.6 32.4 33.4 Tensile strain (%) -- 68.6 70.0 72.0 Modulus (kpsi)
-- 524 471 448 Shrinkage (%) -- 17.5 19.9 19.5 143.degree. C. Haze
-- 0.72 0.77 0.61 Transmittance (%) -- 91.9 92.6 92.2 Clarity --
97.8 97.4 98.9 Gloss 20 -- 47.1 89.4 84.3 45 -- 86.2 86.2 91.7 60
-- 127.2 126.3 126.4 Tensile stress (kpsi) 33.4 35.6 33.4 32.3
Tensile strain (%) 75.0 77.3 80.0 72.1 Modulus (kpsi) 601 579 561
496 Shrinkage (%) -- 16.16 19.65 18.17 149.degree. C. Haze 1.58
2.63 2.5 6.08 Transmittance (%) 91.2 90.9 91.1 87.2 Clarity 95.3
90.5 91.3 87.1 Gloss 20 44.5 67.1 47.3 46.7 45 88.9 85.8 86.3 79.3
60 113.9 114.4 109.1 103.8 Tensile stress (kpsi) 29.5 27.2 29 24.7
Tensile strain (%) 83.6 65 81.5 66 Modulus (kpsi) 536 470 521 356
Shrinkage (%) 8.3 10.1 9.1 10.1 .sup.afilm broke after yield when
stretched at 138.degree. C.
[0058] The examples provided demonstrate that the addition of RCP
to a homopolymer, which has relatively small amounts of xylene
solubles and is not easily stretchable, facilitates the
stretchability of the homopolymer. Thus it is possible to replace
standard high solubles BOPP grade polypropylene homopolymers with
lower solubles content materials. This is especially advantageous
to produce a stiffer film since a high crystalline PP can be
modified to be stretchable under the conventional processing
conditions. Further, the films produced from the blend containing
RCP exhibit improved properties over films produced with standard
BOPP grade polypropylene.
[0059] The present invention has thus been described in general
terms with reference to specific examples. Those skilled in the art
will recognize that the invention is not limited to the specific
embodiments disclosed in the examples. Those skilled in the art
will understand the full scope of the invention from the appended
claims.
* * * * *